The present invention relates to a check valve, in particular for medical applications, which comprises a first and a second hose connecting casing and a resilient membrane disk that is configured between said casings and that, in the event of excess pressure in an intake channel of the first hose connecting casing can be lifted off an annular valve seat enclosing an surrounding intake space communicating with said intake channel and that, in the event of excess pressure in a discharge channel of the second hose connecting casing, can be pressed reliably and in a minimum of time onto the valve seat, this membrane disk being fitted at its outer periphery with an annular bead received in mutually opposite annular grooves of the hose connecting casings, the membrane disk being fitted radially outside said valve seat and above an annular space surrounding the same with apertures running to a discharge space and the wall of the second hose connecting casing's wall opposite said apertures being fitted with recesses that communicate with the said discharge channel.
Such a check valve is already known from the applicant's earlier disclosure in the German Gebrauchsmuster 20 2004 009 358.8.
Such check valves are needed in medical practice in the conduits of infusion systems, diagnostic apparatus, intravenous hose conduits and the like, and consequently they must close very reliably and their time of closure must be kept within fractions of a second to preclude any reflux of liquids contaminated with undesirable substances. At the same time the manufacture of such check valves must be extremely economical as well as being very accurate when considered statistically, such valves in medical practice being exclusively used as one-way means (non-return articles) and their economically required manufacture entailing automated mass prochannelion. At the same time there are rigorous statutory requirements to assure unvarying and uniform operation, and observance of statutory requirements being monitored for instance in Germany by the Technischen Überwachungsverein (Technical Monitoring Service). Such medical check valves are sanctioned only following appropriate positive test results.
The above defined check valve improves one of an earlier disclosure of applicant in the European patent document 0 612 537. This known valve on one hand fully meets the above cited requirements because its design calls for grooves receiving the annular bead at the periphery of the membrane disk in such a way that when assembling the two hose connecting casings, the said membrane disk shall be subjected to radial tractions allowing adjusting the tension in the membrane, as a result of which the check valve may be made even more quickly and reliably responsive. On the other hand practical operation of this known valve has shown that higher pressures at the check valve's intake side my entail the membrane apertures coming to rest against the opposite wall of the discharge space, thus causing unintended closure of an open check valve.
To remedy this unintended behavior of the membrane and unintended valve closure, another feature of the aforementioned valve is used, namely the second hose connecting casing's wall opposite said apertures has been fitted at said check valve's discharge side with recesses communicating with the discharge channel and configured as an annular channel of a radius corresponding to the radius at which the apertures are configured in the membrane disk. This design features ensures that even if due to high pressures the membrane disk were to be entirely forced against the discharge space's wall, nevertheless the desired flow cross-section shall be preserved, this flow taking place through the annular channel to the discharge side.
Practical operation of the above check valve however has shown that even the above improved design may be sometimes inadequate in the presence of high pressures due to the membrane being distorted so much in this process that the total available open flow cross-section might then be reduced. Another difficulty encountered at high pressures is that after high-pressure relief, the membrane might be excessively stressed and thereby no longer sealing adequately while at the same time the opening pressure has been considerably lowered.
A further improvement to the above check-valve difficulties was attained by means of the design disclosed in applicant's patent document DE GM 20 2006 016 730.7 (Gebrauchsmuster), namely in that the recesses on the membrane disk's discharge side be separated from each other by support faces, the recesses communicating through narrow, deep grooves with the discharge channel. The recess-fitted support faces assume the shape of a kind of crown-shaped protrusion from the second hose connecting casing's opposite wall, which supports the membrane when the valve is opened.
With respect to a check valve of the kind defined above, it is the objective of the present invention to even further improve it relative to the state of the art, namely allowing much higher operational pressures in spite of a low opening pressure.